416 Dr. M. W. Travers on the 



the cold gas passing through F forms an excellent insulator 

 for the liquid-air chambers B and C. 



To support the whole apparatus, and to afford a means of 

 securing the vacuum-vessel H, a collar I is soldered to the 

 tube k and to a tube m 4 inches in diameter, which rests on 

 a flange n in a hole in a shelf attached to the wall o£ the 

 compressor room. The space between m and k is packed 

 with animal wool, as is also the space within the containing- 

 cylinder Q. 



The vacuum-vessel H is of such a diameter that when the 

 coil B and the tube k are covered with a single layer of 

 flannel it exactly fits over them. To make a gas-tight junction 

 a rubber ring, which fills the space between the vacuum-vessel 

 and the inner wall of m, is pressed between a brass ring o 

 and a gland p. The ring o rests on three short studs on the 

 inside of m, and the gland is forced home by three nuts and 

 screws qq which are fixed at their upper ends into the 

 flange n. 



When the gland is in position the only means by which gas 

 or liquid can escape from the apparatus is by the tube G, or 

 through the opening at the bottom of the vacuum-vessel H. 

 It is, of course, intended to draw off the liquid at the latter 

 opening, and as it is quite impossible to employ a stopcock 

 for the purpose, the following arrangement has been adopted. 

 The vacuum-vessels H and K are both enclosed in a glass 

 tube LL, which is closed at the bottom and is connected at 

 the top by a rubber sleeve s to a brass tube h which forms 

 part of the gland p; a short copper tube is soldered into s and 

 terminates in a stopcock r. When r is closed any liquid 

 formed at the valve E is retained in H ; but when r is opened 

 the liquid can flow into K, as the gas produced by its evapora- 

 tion can then escape. The lower part of the tube L is enclosed 

 in a large vacuum-vessel M, which contains a small quantity 

 of liquid air during the experiment ; it serves rather to 

 prevent the frosting of the outside of L than to exclude heat. 



The hydrogen escaping from G passes through the rubber 

 tube iv into the tube R, which communicates directly with the 

 cylinder P (text-fig.) and through the stopcock i with the 

 main supply-pipe N connecting the gasometer and the com- 

 pressor. The cylinder P is of sheet zinc, and is soldered to the 

 three brass tubes R, S, and T. The tube S, which is lined 

 with glass and has a window in front and behind, contains the 

 nozzle of the tube leading from the cylinder /x in which the 

 water used to lubricate the cylinder of the compressor is 

 separated; this arrangement prevents the loss of the gas 

 which escapes each time the water is discharged. The tube T 



